ADT7467 Analog Devices, Inc., ADT7467 Datasheet - Page 15

• Manufacturer Part Number: ADT7467
• Description: Dbcool Remote Thermal Monitor And Fan Controller
• Manufacturer: Analog Devices, Inc.

ANALOG-TO-DIGITAL CONVERTER
All analog inputs are multiplexed into the on-chip, successive
approximation, analog-to-digital converter, which has a resolu-
tion of 10 bits. The basic input range is 0 V to 2.25 V, but the
input has built-in attenuators to allow measurement of V
without any external components. To allow for the tolerance of
the supply voltage, the ADC produces an output of 3/4 full scale
(decimal 768 or 300 hex) for the nominal input voltage and,
therefore, has adequate headroom to deal with overvoltages.
VOLTAGE MEASUREMENT INPUT
The ADT7467 has one external voltage measurement channel.
It can also measure its own supply voltage, V
measure V
out through the V
Register 1 (Reg. 0x40) allows a 5 V supply to power the
ADT7467 and be measured without overranging the V
measurement channel. The V
chipset supply voltage in computer systems.
Input Circuitry
The internal structure for the V
Figure 22. The input circuit consists of an input protection
diode, an attenuator, and a capacitor to form a first-order low-
pass filter that gives the input immunity to high frequency
noise.
Voltage Measurement Registers
Reg. 0x21 V
Reg. 0x22 V
V
Associated with the V
high and low limit register. Exceeding the programmed high or
low limit causes the appropriate status bit to be set. Exceeding
either limit can also generate SMBALERT interrupts.
Reg. 0x46 V
Reg. 0x47 V
Reg. 0x48 V
Reg. 0x49 V
Table 6 shows the input ranges of the analog inputs and output
codes of the 10-bit ADC.
CCP
Limit Registers
CCP
CCP
CC
CCP
CCP
CC
CC
V
. The V
CCP
reading = 0x00 default
low limit = 0x00 default
high limit = 0xFF default
reading = 0x00 default
low limit = 0x00 default
high limit = 0xFF default
Figure 22. Structure of Analog Inputs
CC
pin (Pin 3). Setting Bit 7 of Configuration
CC
CCP
17.5kΩ
supply voltage measurement is carried
and V
52.5kΩ
CCP
CC
CCP
input can be used to monitor a
measurement channels is a
analog input is shown in
35pF
CC
. Pin 14 can
CC
CCP
Rev. A| Page 15 of 80
When the ADC is running, it samples and converts a voltage
input in 0.7 ms and averages 16 conversions to reduce noise; a
measurement takes nominally 11 ms.
ADDITIONAL ADC FUNCTIONS
FOR VOLTAGE MEASUREMENTS
A number of other functions are available on the ADT7467 to
offer the system designer increased flexibility.
Turn-Off Averaging
For each voltage measurement read from a value register,
16 readings are made internally, the results of which are averaged
and then placed into the value register. For instances where faster
conversions are needed, setting Bit 4 of Configuration Register 2
(Reg. 0x73) turns averaging off. This produces a reading that is
16 times faster (0.7 ms), but the reading may be noisier.
Bypass Voltage Input Attenuator
Setting Bit 5 of Configuration Register 2 (Reg. 0x73) removes
the attenuation circuitry from the V
user to directly connect external sensors or to rescale the analog
voltage measurement inputs for other applications. The input
range of the ADC without the attenuators is 0 V to 2.25 V.
Single-Channel ADC Conversion
Setting Bit 6 of Configuration Register 2 (Reg. 0x73) places the
ADT7467 into single-channel ADC conversion mode. In this
mode, the ADT7467 can be made to read a single voltage
channel only. If the internal ADT7467 clock is used, the selected
input is read every 0.7 ms. The appropriate ADC channel is
selected by writing to Bits <7:5> of the TACH1 minimum high
byte register (Reg. 0x55).
Table 5. Programming Single-Channel ADC Mode
Bits <7:5> Reg. 0x55
001
010
101
110
111
Configuration Register 2 (Reg. 0x73)
<4> = 1, averaging off
<5> = 1, bypass input attenuators
<6> = 1, single-channel convert mode
TACH1 Minimum High Byte (Reg. 0x55)
<7:5> selects ADC channel for single-channel convert mode.
Channel Selected
V
V
Remote 1 temperature
Local temperature
Remote 2 temperature
CCP
CCP
CC
input. This allows the
ADT7467